Method for preparing biodegradable microcapsules and microcapsules obtained in this manner

ABSTRACT

Method for manufacturing microcapsules enclosing a substance referred to as the active substance, in which method: there are provided an aqueous solution of a surfactant, an oily phase comprising the active substance and at least a first monomer X, and a polar phase having at least a second monomer Y; an O/W emulsion is prepared by adding the oily phase to the aqueous solution of the surfactant; the polar phase is added to the O/W emulsion in order to obtain a polymer by polymerisation of the X and Y monomers; starting from this reaction mixture, the microcapsules are isolated and comprise a wall which is formed by the polymer and which encloses the active substance; the polymer is a poly(beta-amino ester).

TECHNICAL FIELD OF THE INVENTION

The present description relates to the field of microcapsules, and moreparticularly to methods for manufacturing microcapsules with a view toenclosing active substances actives such as essential oils. Morespecifically, it relates to a method for preparing biodegradablemicrocapsules. This method performs interfacial polymerization ofmultifunctional compounds resulting in poly(beta-amino ester)s. Theinvention also relates to biodegradable microcapsules obtained with thismethod.

RELATED ART

Microencapsulation is a method for protecting a reactive, sensitive orvolatile substance (referred to here as “active ingredient”) in acapsule in which the size can vary from a nanometer to a micrometer. Thecore of the capsule is therefore isolated from the external environmentthereof by a wall. This makes it possible to delay the evaporation,release or degradation thereof; there are numerous applications whichmake use of these technical effects when the microcapsules areincorporated in a complex formulation or applied to a product.

For example, microcapsules can be used to disperse in a controlledmanner the active ingredient contained therein, which can particularlybe a biocidal agent, an insecticide, a disinfectant, or a fragrance;this can take place by diffusion through the wall or under the influenceof an external force which ruptures the wall.

In some applications, the release of the active ingredient takes placeunder the influence of an external force which breaks the wall of themicrocapsules; thus, it is possible to release an adhesive (see forexample WO 03/016369—Henkel), or a reagent (see for example WO2009/115671—Catalyse).

In further applications, the contents of the microcapsule cannot escapebut the color change thereof under the effect of a variation oftemperature (thermochromism) or of UV radiation (photochromism) isoutwardly visible (see for example WO 2013/114 025—Gem Innov, or WO2007/070118—Kimberly-Clark, or EP 1 084 860—The Pilot Ink Co.).

There are several techniques for preparing microcapsules. The main onesare spray-drying, interfacial polymerization, solvent evaporation,polymer self-assembly using the Layer-by-Layer (LbL) technique, andcolloidosome preparation. All these techniques make it possible toobtain stable microcapsules of a mean diameter of 10 μm. Interfacialpolymerization is nevertheless the predominant technique as it enablesquick preparation in a single step of microcapsules in which the wall ifstrong enough for the latter to be isolated and thus be used in numerousapplications.

The formation of microcapsules by interfacial polymerization is usuallyperformed in 4 steps: (i) Preparing a first phase containing the activeingredient (for example an essential oil) and an organo-soluble monomer;(ii) Forming an emulsion by dispersing first phase in an aqueous mediumcontaining surfactant, and which represents the second phase; (iii)Adding the water-soluble monomer to the second phase; (iv) Forming andmaturing the membrane by reacting the monomers by polycondensation atthe interface.

Several polymer families are conventionally used for manufacturing thewall of microcapsules (Perignon, C. et al., Journal ofMicroencapsulation 2015, 32 (1), 1-15), such as polyamides (PA),polyurethanes (PU) or polyureas. The preparation of PA microcapsulewalls generally uses monomers of the diamine (hexamethylene diamine forexample) and acyl chloride (sebacoyl chloride for example) type, whereasthose in PU make use of monomers of the di-isocyanate (HDI, IPDI etc.)and diol type. In the case of polyureas, di-isocyanate and diamine typemonomers or di-isocyanates alone are used wherein the hydrolysis at theinterface produces amines enabling urea function synthesis.

For example, the document WO 2009/115671 cited above describes theformation of microcapsule walls by interfacial polycondensation, usingdifferent monomer mixtures: hexamethylene diisocyanate (HMDI) andethylene diamine; tetraethylorthosilicate (TEO) and3-(trimethoxysilyl)propylmethacrylate (MPTS); 2,4-tolylenediisocyanate(TDI) and 1,3 phenylenediamine; 2,4-toluene diisocyanate and1,3-phenylene diamine.

There are already some works reporting the preparation of microcapsulesby interfacial polymerization using other types of polymers. Mention canbe made for example of the works by J. Bernard on the preparation ofglyconanocapsules by copper-catalyzed azide-alkyne cycloaddition (R.Roux et al., J. ACS Macro Lett. 2012, 1 (8), 1074-1078), or the works byK. Landfester (Siebert et al. Chem. Commun. 2012, 48, 5470-5472). L. Shiet al. (J. Appl. Polym. Sci. 2016, 133 (36), 168-7) and D. Patton et al.(ACS Appl. Mater. Interfaces 2017, 9 (4), 3288-3293) who also preparedmicrocapsules by thiol-ene chemistry initiated by respectively a baseand a photoinitiator.

A relatively broad spectrum of polymeric materials is therefore proposedto a person skilled in the art to select the suitable type ofmicrocapsule for a given use. Thus, microcapsules are already used innumerous technical applications, but the application potential thereofhas not yet been fully recognized, and it is a strongly emerging sectordestined to grow significantly once the microcapsule wall meetsincreasingly stringent criteria in terms of toxicity and recyclability.

However, microcapsules represent microparticles of polymeric materials.For some years, polymeric material microparticles have been identifiedas an area of environmental concern, due to the wide disseminationthereof in ecosystems, in soils, in aquatic and maritime ecosystems,reaching distant locations from the place where they were introducedinto the ecosystem. This wide dissemination harms not only as a generalrule the organisms present in these ecosystems, but could also haveharmful effects for human health. Increasingly stringent regulations arealready being announced which restrict the use of plastics capable offorming microparticles during the degradation thereof in-situ in anatural environment, and especially of plastics used directly in theform of microparticles.

For environmental reasons, it may seem contradictory to seek to developa novel product consisting of polymeric microparticles. It has henceemerged as desirable to have microcapsules made of degradable polymericmaterial. It is noted that microcapsules, used in numerous specialapplications and capable of being incorporated in numerous products incommon use (such as textile materials, cosmetic or phytosanitaryproducts) or technical use (such as paints, varnishes, inks), will notnormally undergo end-of-life collection, and therefore cannot undergobiodegradation by composting, as can be envisaged for collected plasticproducts. Thus, the degradability of the plastics forming the wall ofmicrocapsules cannot be based on chemical mechanisms which take placeduring composting. In this context, the question as to whether thedegradability of the microcapsules involves a biological mechanism issomewhat unimportant; what is important is the degradability thereof inan ecosystem, regardless of the chemical mechanism of this degradation.For example, a fermentation would be a biodegradation, while a simpledegradation in an ecosystem under the effect of light could be aphotochemical reaction independent of the ecosystem; in reality, thesituation will often be a combination, especially if the degradationtakes place in stages. We use the expression “(bio)degradable”hereinafter to denote the characteristic of a material of degrading in anatural environment on a relatively brief scale (of the order of weeksor a year), according to the characteristics of this natural environmentand the exposure of the material to the various agents present in thisnatural environment.

It is observed that all the microcapsules previously developed result inthe preparation of polymer chains (polyamide, polyurea, polyurethane,etc.) which will be either physically interlocked in the case of areaction between bifunctional compounds, or crosslinked in the case ofone or more multifunctional compounds (functionality 3). In any case,the walls are not (bio) degradable due to the nature of the polymerchain. The problem addressed by the present invention is that ofproviding a novel type of microcapsules, which is easy to synthesize,without making use of toxic and/or costly raw materials, is(bio)degradable in the natural environment, can be used with a largenumber of active ingredients, and provides good external protection forthe active ingredient that it is intended to contain.

Subject Matter of the Invention

During their research work, the inventors discovered that onepossibility for obtaining degradable microcapsules would be to preparewalls made of polyester, which is a polymer known for the(bio)degradability thereof. The literature shows that studies havealready been conducted on this theme, and it has been demonstrated thatthe rate of reaction between acid chlorides and diols was very slow.This system is thus unsuitable for interfacial polymerization (see E. M.Hodnett and D. A. Holmer, J Polym Sci, 1962, 58, 1415-21). Specificconditions such as the use of bisphenol A as diol and/or a reaction atvery high pH made it possible to obtain microcapsules (see W. Eareckson,J Polym Sci, 1959, 399-406; see also P. W. Morgan and S. L. Kwolek, JPolym Sci, 1959, 299-327) but these conditions are overly restrictivefor numerous internal phases and/or applications. Furthermore, the slowrate of polymerization reactions impedes the industrial use thereof ineconomic terms and in terms of short or even continuous productioncycles.

Thus, the inventors did not pursue this avenue. According to theinvention, the problem is solved using microcapsules made ofpoly(beta-amino)ester (abbreviated here as PBAE). According to theinvention, these microcapsules are synthesized in a single reaction stepvia an addition reaction of amine functions to acrylate functions(reaction known as “Michael addition”), by interfacial polymerization.This reaction results in the micro-encapsulation of the organic phasewithout forming by-products (see reaction diagram in FIG. 6). Thepresence of ester functions in the PBAE backbone gives the polymer gooddegradation properties via hydrolysis.

Poly(beta-amino ester)s are known per se and have been usedsubstantially in recent years (Lynn, D. M.; Langer, R. J. Am. Chem. Soc.2000, 122 (44), 10761-10768; Liu, Y.; Li, Y.; Keskin, D.; Shi, L. Adv.Healthcare Mater. 2018, 2 (2), 1801359-24) thanks to thebiocompatibility and biodegradability properties thereof, and they nowrepresent a family of materials which have numerous applications asbiomaterials (for example as anticancer drug vector, as antimicrobialmaterial, and for tissue engineering).

The areas of application of poly(beta-amino ester)s are very vast (seeFIG. 9).

Generally, it is known that aza-Michael addition type reactions can beperformed in a wide range of solvents ranging from halogenated nonpolarsolvents (dichloromethane or chloroform for example) to polar solventssuch as dimethyl sulfoxide (DMSO) for example (Liu, Y.; Li, Y.; Keskin,D.; Shi, L. Adv. Healthcare Mater. 2018, 2 (2), 1801359-24). Inpractice, the PBAEs are essentially prepared in solution and aresubsequently formulated to produce for example micelles, particles,gel/hydrogels, or films (so-called Layer-by-Layer technique).Oligo-PBAEs have also been crosslinked in a second phase, either byphotopolymerization (Brey, D. M.; Erickson, I.; Burdick, J. A. J.Biomed. Mater. Res. 2008, 85A (3), 731-741.7), or in the presence ofdi-isocyanates.

It is also known that linear or crosslinked PBAEs are relatively stablein neutral medium but are degraded more rapidly by ester functionhydrolysis at acid and/or basic pH. This hydrolysis phenomenon resultsin the release of small molecules such as bis(β-amino acid)s and diolswhen linear PBAEs are used; these molecules are known to be non-toxicwith respect to mammalian cells, and to have a weak influence on themetabolism of healthy cells.

According to an essential feature of the present invention, themicrocapsules having a PBAE wall are synthesized by interfacialpolymerization.

More specifically, according to the invention, the problem is solved bya method wherein the Michael polycondensation reaction between aminefunctions and acrylate functions is used to obtain Poly(Beta-AminoEsters) (PBAEs) by interfacial polymerization. The inventors discoveredthat this method, applicable to various active ingredients to beencapsulated, makes it possible to prepare stable microcapsules capableof being isolated by drying and which have the property of being (bio)degradable.

The microencapsulation method according to the invention comprises thefollowing steps:

(a) Dispersion of one or more compounds having at least two acrylatefunctions in an organic solution (also referred to here as “oily phase”,in the context of an emulsion) forming the phase to be encapsulated (andcomprising, where applicable, the active ingredient);

(b) Addition of an excess with respect to the preceding volume of anaqueous phase comprising one or more surfactants, followed by anemulsification;

(c) Addition to the emulsion obtained in step (b) of one or morecompounds including at least one primary amine function and/or twosecondary amine functions and polymerization reaction at a temperaturebetween about 20° C. and 100° C.;

(d) Collection, washing and drying of the microcapsules.

Thus, the invention firstly relates to a method for manufacturingmicrocapsules containing a so-called active substance, in which method:

an aqueous solution of a surfactant, an oily phase comprising saidactive substance and at least a first monomer X, and a polar phasecomprising at least a second monomer Y are provided;

an O/W type emulsion is prepared by adding said oily phase to saidaqueous solution of the surfactant;

said polar phase is added to said O/W emulsion, in order to obtain apolymer by polymerizing said monomers X and Y;

from this reaction mixture, said microcapsules including a wall formedby said polymer and containing said active substance are isolated;

said method being characterized in that said polymer is apoly(beta-amino ester).

Said first monomer X is selected from (multi)acrylates, particularly(multi)acrylates of formula X′—(—O(C═O)—CH═CH₂)_(n) where n≥2 and whereX′ is a molecule whereon n acrylate structural units are grafted.

Said first monomer X is, preferably, selected from (multi)acrylates offormula X′—(—O(C═O)—CH═CH₂)_(n) where n≥4 and where X′ is a moleculewhereon n acrylate structural units are grafted. More specifically, itis advantageously selected from the group formed by:

diacrylates, and preferably those described in the article by Nayak etal. (Polymer-Plastics Technology and Engineering, 2018, 57, 7, 625-656);

triacrylates, particularly C₁₅O₆H₂O (CAS No. 15625-89-5, i.e.trimethylolpropane triacrylate), tetraacrylates, pentaacrylates,hexaacrylates, mixtures of these different acrylates of typeO[CH₂C(CH₂OR)₃]₂ where R is H or COCH═CH₂;

(multi)acrylates described in the article by Nayak et al.(Polymer-Plastics Technology and Engineering, 2018, 57, 7, 625-656);

polymers carrying pendant acrylate functions;

functional oligo-PBAEs, prepared for example by reacting diacrylatecompounds with a functional primary amine and/or a functional secondarydiamine;

the mixture of different compounds described above.

Said second monomer Y is selected from amines. More specifically, it isadvantageously selected from the group formed by:

primary amines R—NH₂;

primary diamines of type NH₂(CH₂)_(n)NH₂ where n is an integer which cantypically be between 1 and 20, and

which is preferably 2 or 6;

secondary diamines comprising an aromatic core such as meta-xylylenediamine;

primary (multi)amines such as tris(2-aminoethyl) amine;

secondary diamines such as piperazine;

(multi)amines containing primary and secondary amine functions such astetraethylene pentamine;

polymers containing primary and/or secondary amine functions such aspolyethylene imine.

In an embodiment, said polymerization of said monomers is performedunder stirring at a temperature between 20° C. and 100° C., andpreferably between 30° C. and 90° C.

The invention further relates to a microcapsule containing a so-calledactive substance, characterized in that the wall thereof consists ofpoly(beta-amino ester).

The invention further relates to a microcapsule that can be obtainedwith the method according to the invention.

The wall of the microcapsules thus prepared can be modified by adding apolymer layer deposited on the surface of the microcapsules. Thisdeposition can be performed by adding a polymer dispersed in an aqueousphase which will be deposited on the surface of the capsules. Amongthese polymers, mention can be made of polysaccharides (for example,cellulose, starch, alginates, chitosan) and derivatives thereof.

Another possibility for modifying the wall of the microcapsules is thatof modifying it by adding a radical initiator either in the aqueousphase or in the oily phase. A final possibility is that of reacting theresidual surface amine functions with water-soluble monofunctionalacrylates to modify the surface condition of the microcapsules.

FIGURES

FIGS. 1 to 18 illustrate certain aspects of the invention, but do notrestrict the scope thereof. FIGS. 2 to 5 refer to example 1. FIG. 7refers to example 2, FIG. 8 to example 3, FIG. 8 to example 3, FIG. 10to example 6, FIG. 11 to example 7, FIG. 12 to example 10, FIG. 13 toexample 11, FIG. 14 to example 13, FIG. 15 to example 14, FIG. 16 toexample 15, FIG. 17 to example 17, and FIG. 18 to example 18.

FIGS. 2 to 5 and 10 to 14 are optical micrographs; the horizontal bar atthe bottom left of the image represents a length of 50 82 m. FIGS. 17and 18 are also optical micrographs.

FIG. 1 shows the general diagram of the method according to theinvention. The four-digit reference numbers denote steps of this method.

FIG. 2 shows an optical micrograph of microcapsules obtained accordingto example 1, after 5 hours of reaction.

FIG. 3 shows a Fourier transform infrared (FTIR) spectrum of the wall ofthe microcapsules isolated in slurries after 6 hours of reaction.

FIG. 4 shows an optical micrograph of microcapsules obtained accordingto example 1, after drying on a glass strip.

FIG. 5 shows two optical micrographs of microcapsules obtained accordingto example 1, after drying on a glass strip. The left micrograph wasobtained in grazing incidence light, the right micrograph underfluorescent light after adding some drops of a fluorescent dye.

FIG. 6 illustrates the reaction diagram of the reaction according to theinvention.

FIG. 7 shows that the thermochromic microcapsules are stable after a30-min oven passage and that the thermochromic function thereof ispreserved.

FIG. 8 illustrates the degradability of the walls of the microcapsulewith an accelerated degradation test.

FIG. 9 illustrates the different fields of application ofpoly(beta-amino ester)s.

FIG. 10 shows that the microcapsules are stable after 24 hours, and themean diameter thereof is between 10 μm and 30 μm.

FIG. 11 shows a similar image to FIG. 10, and leads to the sameconclusion, for another example.

FIG. 12 shows the result of the use of the microcapsules according tothe invention in a carbonless copy paper.

FIG. 13 shows a photograph of microcapsules according to another exampleof the invention.

FIG. 14 shows a photograph of microcapsules according to another exampleof the invention.

FIG. 15 shows the biodegradation percentage as a function of time fordry microcapsules according to the invention.

FIG. 16 shows the biodegradation percentage as a function of time forthe wall of the microcapsules according to the invention.

FIG. 17 shows a photograph of microcapsules according to another exampleof the invention.

FIG. 19 shows a photograph of a cotton fiber which has been placed incontact with microcapsules according to the invention in which thesurface has been modified (b) or not (a).

DETAILED DESCRIPTION

In the following detailed description of embodiments of the presentdescription, numerous specific details are disclosed in order to providea more in-depth understanding of the present invention, and to enable aperson skilled in the art to execute the invention. However, it will beobvious to a person skilled in the art that the present description canbe implemented without these specific details. In other cases,well-known features have not been described in detail to avoidoverburdening the description unnecessarily.

FIG. 1 shows a general diagram of the method according to the invention.The aqueous surfactant solution (1000) is prepared. An organic solution(also known as “oily phase”) is also prepared comprising the phase to beencapsulated (which comprises the so-called active substance) and themonomer X (1002). At step 1010, this oily phase 1002, which is anorganic solution, is added to said aqueous solution 1000 and at step1020 an O/W (oil-in-water, according to a term known to a person skilledin the art) type emulsion 1022 is obtained. In this emulsion, saidorganic solution is the so-called oily phase (O phase). At step 1030, anaqueous solution of the monomer Y 1024 is added to said emulsion 1022.At step 1040, the polymerization reaction results in a reaction mixture1042 from which, at step 1050, a heterogenous mixture 1052 known asslurry is formed, which comprises, suspended in an aqueous base, themicrocapsules containing the phase to be encapsulated.

Step 1050 involves as a general rule a temperature of the reactionmixture 1042 greater than about 20° C., typically between 20° C. and100° C. A temperature between about 30° C. and about 90° C. ispreferred, and even more preferably between about 40° C. and about 80°C.

This method can be applied to different monomers X and Y. According tothe invention, the monomer X is a (multi)acrylate, and the monomer Y isan amine, preferably, a primary amine and/or a primary (multi)amineand/or a secondary diamine and/or a compound having primary andsecondary amines.

The term (multi)acrylate denotes any compound of formulaX′—(—O(C═O)—CH═CH₂)_(n) where n≥2 and where X′ is a molecule whereon nacrylate structural units are grafted.

The term primary (multi)amine denotes any compound comprising at leasttwo primary amine functions.

As an acrylate, it is possible to use for example triacrylates (such asC₁₅O₆H₂O, CAS No. 15625-89-5); tetraacrylates; pentaacrylates;hexaacrylates; mixtures of these different acrylates cited. It ispossible to use for example molecules of type O[CH₂C(CH₂OR)₃]₂ where Rcan be H or COCH═CH₂.

As an amine, it is possible to use for example molecules of typeNH₂(CH₂)_(n)NH₂ where n is an integer which can typically be between 1and 20, and which be for example 2 (ethylene diamine) or 6(hexamethylene diamine, CAS number: 124-09-4). It is also possible touse piperazine, meta-xylylene diamine, pentaethylenehexamine,tris(2-aminoethyl)amine (TREN) or polyethylene imine (PEI).

The nature and the concentration of the amines and the acrylates can bevaried.

The reagent function ratio of the monomers Y (—NH) and X (acrylate) isadvantageously greater than 1, and typically between 1 and 5, preferablybetween 1.2 and 3.8.

According to a specific embodiment of the invention, the monomers X(acrylate) and/or Y (amine) are biosourced.

FIG. 6 shows the reaction diagram of the aza-Michael addition reactionbetween a secondary amine and an acrylate (reaction (a)) and thepolyaddition reaction between a multifunctional acrylate compound and amulti-amine compound resulting in a cross-linked polymer (reaction (b)).

The organic core of the microcapsules can consist of an organic phasecomprising an active substance. During the formation of themicrocapsule, this organic (oily) phase will be enclosed by thepolymeric wall of the microcapsule, which protects it from theenvironment. Said organic (oily) phase can consist of said activesubstance, or said active substance can be part of said organic (oily)phase, wherein it can be particularly dissolved. The expression “activesubstance” refers here to the specific purpose wherein the microcapsulesare intended to be used; as a general rule, in view of the specificityof the microcapsule product, this purpose is always known during themanufacture thereof.

The active substance can be selected particularly from oils (pure orcontaining possibly other molecules in solution or in dispersion), suchas essential oils, natural and edible oils, plant and edible oils,liquid alkanes, esters and fatty acids, or from dyes, inks, paints,thermochromic and/or photochromic substances, fragrances, products withbiocidal effect, products with fungicidal effect, products withantiviral effect, products with phytosanitary effect, pharmaceuticalactive ingredients, products with cosmetic effect, adhesives; theseactive ingredients being optionally in the presence of an organicvector.

It is possible to use, non-restrictively, distillation extracts ofnatural products such as essential oils of eucalyptus, citronella,lavender, mint, cinnamon, camphor, aniseed, lemon, orange, which can beobtained by extraction from plant matter, or by synthesis.

It is also possible to use other substances such as long-chain alkanes(for example tetradecane), which can contain lipophilic solutions insolution.

As a general rule, and according to the function sought for themicrocapsules, it is possible to use any hydrophobic compound, whichwill thus be naturally dispersed in the form of emulsion of hydrophobicdroplets suspended in an aqueous phase.

Numerous additives enabling superior protection of the organic (oily)phase to be encapsulated, against infrared radiation, ultravioletradiation, unintentional entry of specific gas or oxidation, can beincorporated in the microcapsule.

The wall of the microcapsules can be modified by adding a coating on thesurface thereof. This deposition can be performed by adding a polymerdispersed in an aqueous phase which will be deposited on the surface ofthe capsules. Of these polymers, mention can be made of polysaccharides(cellulose, starch, alginates, chitosan, etc.) and derivatives thereof.This addition can be performed either hot or at ambient temperature atthe end of the interfacial polymerization step.

The wall of the microcapsules can also be modified by adding a radicalinitiator either in the aqueous phase or in the organic (oily) phase.The addition in the organic phase can be performed before and/or afterpreparing the PBAE wall. If the addition is performed afterwards, theradical initiator can be diluted in acetone to promote transport in themicrocapsules. These initiators can be azo compounds (such asazobis-isobutyronitrile and derivatives thereof) or peroxide compounds(lauroyl peroxide, etc.). In the case of initiators added in the aqueousphase, they can consist particularly of water-soluble azo compounds(such as 2,2′-Azobis(2-methylpropionamidine)dihydrochloride) red-oxsystems (ammonium or potassium persulfate in combination with potassiummetabisulfate for example). In an inert atmosphere, the radicals fromthe decomposition of the radical initiators can be added to the residualacrylate functions of the PBAE wall and reinforce it mechanically and/ormodify the polarity thereof.

Another way to modify the wall of the microcapsules is to react theresidual surface amine functions with water-soluble monofunctionalacrylates. Without wishing to be bound to this hypothesis, the inventorsbelieve that via Michael addition, an amino-ester bond would be formedand would anchor a functional group on the surface. Of the water-solubleacrylates suitable for use, mention can be made of acrylic acid,2-carboxyethyl acrylate, 2-(dimethylamino) ethyl acrylate,2-hydroxyethyl acrylate, poly(ethylene glycol) acrylates, 3-sulfopropylacrylate potassium salt.

As surfactant, it is particularly possible to use those which are citedin Encyclopedia of Chemical Technology, volume 8, pages 912 to 915, andwhich have a hydrophilic-lipophilic balance (according to the HLBsystem) equal to or greater than 10.

Other macromolecular surfactants can also be used. Mention can be madefor example of polyacrylates, methylcelluloses, carboxymethylcelluloses,polyvinyl alcohol (PVA) optionally partially esterified or etherified,polyacrylamide or synthetic polymers having anhydride or carboxylic acidfunctions such as ethylene/maleic anhydride copolymers. Preferably,polyvinyl alcohol can be used as a surfactant.

It may be necessary, for example in the case of aqueous solutions of acellulose compound, to add a little alkaline hydroxide such as sodiumhydroxide, in order to facilitate the dissolution thereof; suchcellulose products can also be used directly in the form of the sodiumsalts thereof for example. Pluronics type amphiphilic copolymers canalso be used. Generally, aqueous solutions containing from 0.1 to 5 wt.% of surfactant are used.

The size of the droplets is dependent on the nature and theconcentration of the surfactant and the stirring speed, the latter beingchosen particularly high in that smaller mean droplet diameters aresought.

In general, the stirring speed during the preparation of the emulsion isfrom 5000 to 10,000 rpm. The emulsion is usually prepared at atemperature between 15° C. and 95° C. Generally, when the emulsion hasbeen obtained, impeller stirring is stopped and the emulsion is stirredusing a common type of slower stirrer, for example of the frame stirrertype, typically at a speed of the order of 150 to 1500 rpm.

The method according to the invention thus results in homogeneous andfluid suspensions containing, according to the fillers introduced,generally from 20 wt. % to 80 wt. % of microcapsules having a meandiameter of 100 nm to 100 μm. The diameter of the microcapsules can bepreferably between 1 μm and 50 μm, and more preferably between 10 μm and40 μm.

The microcapsules, and in particular the wall thereof, according to theinvention are (bio)degradable. The biodegradation can be determined forexample by one of the methods described in the document “OECD Guidelinesfor Testing of Chemicals: Ready Biodegradability” (adopted by the OECDCouncil on Jul. 17, 1992). The manometric respirometry test (method 301F) can preferably be used. Preferably, this test is used on emptied andwashed microcapsules, so that the biodegradation of the content of themicrocapsules does not interfere with the test which is aimed atcharacterizing the biodegradation of the material forming the wall ofthe microcapsules. Preferably, the microcapsule according to theinvention, and/or the wall thereof, shows a biodegradation of at least80%, preferably at least 83%, more preferably at least 85%, measuredafter 10 days of incubation using said method 301 F. With the samemethod, after 28 days of incubation, the microcapsules according to theinvention preferably show a biodegradation of at least 90%, preferablyat least 95%, and more preferably at least 98%.

EXAMPLES

To allow a person skilled in the art to reproduce the invention,examples of implementation are given here; they do not restrict thescope of the invention.

Example 1 Preparation of Fragranced Microcapsules Based on a Diamine(HMDA)

(i) Emulsion Preparation

11.0 g of essential oil (Eucalyptus) was placed in a beaker, and themulti-acrylate monomer (Dipentaerythritol penta-/hexa-acrylate mixture)(0.39 g, 0.71 mmol) was dispersed in the essential oil under magneticstirring (350 rpm). Stirring was maintained until the solution becomehomogeneous; a heating step was added if required.

The essential oil/organic monomer assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturraxm IKA T10 at 9500 rpm for 3min at ambient temperature to form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, preheated to 50° C., the previously prepared emulsion wasintroduced and stirred at a speed of 250 rpm. When the emulsion reached50° C., the solution of diamine (Hexamethylene diamine HMDA) (0.17 g,1.46 mmol) in 5 g of PVA 2 wt % solution was added dropwise using asyringe and under stirring (250 rpm). During the reaction, samples atdifferent reaction times were taken and analyzed by optical microscopyand Fourier transform infrared (FTIR) spectroscopy in order to monitorthe formation of the microcapsules.

The total quantity of monomers used was ˜0.56 g. The amine was used inexcess with respect to the acrylate monomer so as to obtain a—NH/acrylate function ratio=1.6. The essential oil/water mass ratio isequal to 0.24. The microcapsules can be analyzed by microscopy after adrying step. This analysis makes it possible to ensure the stability ofthe microcapsules once isolated. A second analysis consists of addingsome drops of a fluorescent dye (Nile Red) on the dried microcapsules.Nile Red, a lipophilic chromophore which only fluoresces in an organicphase, makes it possible to verify that the core of the microcapsulestill contains organic phase and that the microcapsules are filled.

FIG. 2 shows an optical microscopy image of the reaction medium after 5hours of reaction. The microcapsules are spherical, with a diameterbetween about 10 μm and about 25 μm. FIG. 3 shows the FTIR spectrum ofthe microcapsules isolated from a slurry after 6 hours of reaction(after washing with acetone, followed by three centrifugation cycles andoven drying). Characteristic vibrations of N—H bonds are observed around3300 cm⁻¹ to 3400 cm⁻¹, along with a narrow band characteristic of a C═Obond around 1727 cm⁻¹.

FIG. 4 shows an optical micrograph of microcapsules dried on a glassstrip. The diameter thereof is around 30 μm to 35 μm. FIG. 5 shows amicrograph of microcapsules dried on a glass strip in glazing incidencelight (on left) and in fluorescent light (on right) after adding somedrops of Nile Red fluorescent dye. The intense emission in fluorescentlight shows that the core of the microcapsule contains an organic phase.

Example 2 Preparation of Fragranced Microcapsules Based on a Diamine(HMDA)

(i) Emulsion Preparation

11.0 g of a thermochromic solution (10° blue) was introduced into abeaker, placed in an oil bath and heated to 130° C. under magneticstirring (350 rpm). Stirring was maintained until the thermochromicsolution became homogeneous and transparent. The thermochromic solutionwas cooled, and when the temperature thereof reaches 50° C., the(multi)acrylate monomer (Dipentaerythritol penta-/hexa-acrylate mixture)(0.39 g, 0.71 mmol) is dispersed under magnetic stirring (350 rpm).Stirring is maintained until the solution becomes homogeneous. Thethermochromic/organic monomer assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturrax™ IKA T10 at 9500 rpm for 3min at ambient temperature to form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, preheated to 50° C., the previously prepared emulsion wasintroduced and stirred at a speed of 250 rpm. When the emulsion reached50° C., the solution of diamine (Hexamethylene diamine HMDA) (0.17 g,1.46 mmol) in 5 g of PVA 2 wt % solution was added dropwise using asyringe and under stirring (250 rpm). During the reaction, samples atdifferent reaction times were taken and analyzed by optical microscopy.

The total quantity of monomers used was ˜0.56 g. The amine was used inexcess with respect to the acrylate monomer so as to obtain a—NH/acrylate function ratio=1.6. The thermochromic solution/water massratio equals 0.24.

The dried microcapsules show a reversible color change with a reversiblechange of coloration at a temperature of 10° C. These same capsules can,furthermore, be heated in an oven at 130° C. for 30 min withoutmodifying the thermochromic properties thereof (FIG. 7).

Example 3 Poly(beta-amino ester) Degradability Test

A first degradability test was performed according to the followingprocedure:

(1) Synthesis of poly(beta-amino ester)

In a beaker, the Hexamethylene diamine HMDA monomer (1.0 g, 8.6 mmol)was solubilized in THF (4.0 g) and added to a solution of(multi)acrylate (trimethylolpropane triacrylate) monomer (1.8 g, 6.1mmol) solubilized in 2.5 g of THF. The mixture was placed in a pill boxsubsequently placed in an oil bath at 50° C.

The amine was used in excess with respect to the acrylate monomer so asto obtain a —NH/acrylate function ratio=2.

The polymer retrieved after 5 hours of reaction was washed three timeswith acetone and oven-dried.

(2) Poly(beta-amino ester) Degradation

The degradation of the poly(beta-amino ester) was performed according tothe following protocol:

20 mg of polymer solubilized in 1 mL of a sodium hydroxide solution (3M,in deuterated water D₂O, pH˜14) is introduced into a flask equipped witha magnetic stirrer. As the polymer is crosslinked, it is not soluble inthe aqueous phase.

FIG. 8 shows that the poly(beta-amino ester) is dissolved in the aqueousphase, characterizing an effective degradation of the polymer underthese accelerated degradation conditions.

Example 4 Preparation of Fragranced Microcapsules Based on a Triamine(TREN)

(i) Emulsion preparation

11.0 g of essential oil (Eucalyptus) was placed in a beaker, and themulti-acrylate monomer (Dipentaerythritol penta-/hexa-acrylate mixture)(0.39 g, 0.74 mmol) was dispersed in the essential oil under stirring.The essential oil/organic monomer assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturraxm IKA T10 to form anemulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, the previously prepared emulsion was introduced therein. Anaqueous solution of tris(2-aminoethyl)amine TREN (0.145 g, 0.99 mmol) in5 g of PVA 2 wt % solution was added under stirring at a temperaturebetween 50° C. and 60° C.

Example 5 Preparation of Thermochromic Microcapsules Based on a Triamine(TREN)

(i) Emulsion preparation

11.0 g of a thermochromic solution was introduced into a beaker andstirred hot, the multi-acrylate monomer (Dipentaerythritolpenta-/hexa-acrylate mixture) (0.39 g, 0.74 mmol) was dispersed thereinunder stirring. The thermochromic/organic monomer assembly was addedgradually to the previously prepared aqueous surfactant solution (40 g,PVA 2 wt. %); the mixture was homogenized using an UltraturraxTM IKA T10to form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, the previously prepared emulsion was introduced at a temperatureof about 50° C. to 60° C. An aqueous solution of tris(2-aminoethyl)amine TREN (0.145 g, 0.99 mmol) in 5 g of PVA 2 wt % solution was addedunder stirring at a temperature between 50° C. and 80° C.

Example 6 Preparation of Microcapsules Based on a Biogenic Monomer

(i) Emulsion preparation

11.0 g of essential oil (Eucalyptus) was placed in a beaker, and themulti-acrylate monomer (Dipentaerythritol penta-/hexa-acrylate mixture)(0.39 g, 0.74 mmol) was dispersed in the essential oil under stirring.The essential oil/organic monomer assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturrax™ IKA T10 to form anemulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, the previously prepared emulsion was introduced, the aqueoussolution of diamine (Butane-1,4-diamine (Putrescine)) (0.13 g, 1.47mmol) in g of PVA 2 wt % was added under stirring at a temperaturebetween 50° C. and 60° C.

FIG. 10 shows an optical microscopy image of the capsules after 24 hoursof reaction. The microcapsules are spherical, with a mean diameterbetween about 10 μm and about 30 μm.

Example 7 Preparation of Microcapsules Based on Polyethylene Imine (PEI)

(i) Emulsion Preparation

11.0 g of essential oil (Eucalyptus) was placed in a beaker, and themulti-acrylate monomer (Dipentaerythritol penta-/hexa-acrylate mixture)(0.39 g, 0.74 mmol) was dispersed in the essential oil under stirring.The essential oil/organic monomer assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturraxm IKA T10 to form anemulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, the previously prepared emulsion was introduced. A solution ofpolyethylene imine (PEI) (1.78 g, 1.48 mmol) in 5 g of PVA 2 wt %solution was added under stirring at a temperature between 50° C. and60° C.

FIG. 11 shows optical microscopy images of the capsules after 24 hoursof reaction. The microcapsules are spherical, with a mean diameterbetween about 10 μm and about 30 μm.

Example 8 Preparation of Fragranced Microcapsules (Shell /PI Ratio=3.4%)

(i) Emulsion Preparation

193.6 g of essential oil (Eucalyptus) was placed in a beaker, and themulti-acrylate monomer

(Dipentaerythritol penta-/hexa-acrylate mixture) (4.5 g, 8.5 mmol) wasdispersed in the essential oil under stirring. The essential oil/organicmonomer assembly was added gradually to the previously prepared aqueoussurfactant solution (255.9 g PVA 2 wt. %); the mixture was homogenizedto form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, the previously prepared emulsion was introduced. A solution ofdiamine

(Hexamethylene diamine HMDA) (2.01 g, 17.2 mmol) in 44.1 g of a PVA 2 wt% solution was added under stirring at a temperature between 50° C. and60° C. The whole was left to react for 2 hours at 50° C. and for 5 hoursat 60° C.

20

Example 9 Preparation of Fragranced Microcapsules

(i) Emulsion Preparation

11.0 g of a mixture of 80% Pineapple papaya fragrance (reference RS42370from the company Technicoflor in Allauch (France)) and 20% methylmyristate was placed in a beaker, and the multi-acrylate monomer(Dipentaerythritol penta-/hexa-acrylate mixture) (0.39 g, 0.74 mmol) wasdispersed in the fragrance under stirring. The essential oil/organicmonomer assembly was added gradually to the previously prepared aqueoussurfactant solution (40 g, PVA 2 wt. %); the mixture was homogenizedusing an Ultraturrax™ IKA T10 to form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, the previously prepared emulsion was introduced. A solution ofdiamine (Hexamethylene diamine HMDA) (0.17 g, 1.49 mmol) in 5 g of a PVA2 wt % solution was added under stirring at a temperature between 50° C.and 60° C. The whole was left to react for 2 hours at 50° C. and for 5hours at 60° C.

Example 10 Preparation of Microcapsules for Carbonless Copy Papers(Shell/PI Ration=3.4%)

(i) Emulsion Preparation

193.6 g of an internal phase (Dye) was placed in a beaker, and themulti-acrylate monomer (Dipentaerythritol penta-/hexa-acrylate mixture)(4.5 g, 8.5 mmol) was dispersed in the internal phase under stirring.The whole was added gradually to the previously prepared aqueoussurfactant solution (255.9 g PVA 2 wt. %); the mixture was homogenizedto form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, the previously prepared emulsion was introduced. An aqueoussolution of diamine

(Hexamethylene diamine HMDA) was added, under stirring at a temperaturebetween 50° C. and 60° C.

(iii) Use of the microcapsules in a carbonless copy paper

These microcapsules were applied on a sheet of paper, according to knownmethods, and used in a carbonless copy system. FIG. 12 shows the result,which is fully satisfactory.

Example 11 Preparation of Thermochromic Microcapsules Based onPOSS@octa(acrylate) Monomer

(i) Emulsion Preparation

20.0 g of thermochromic, and polyoctahedral silsesquioxanes borne byeight acrylate functions (POSS@octa(acrylate), CAS No. 1620202-27-8,purchased from Hydridplastics, 1.48 g, 1.12 mmol) and Butylated

HydroxyToluene (BHT, 5.0 mg) thermal inhibitor, were placed in a beaker.The mixture was solubilized hot under magnetic stirring. Stirring wasmaintained until the solution became homogeneous. Thethermochromic/POSS@octa(acrylate) assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturra™ IKA T10 to form anemulsion.

(ii) Microencapsulation

In a reactor, the previously prepared emulsion was introduced. Thesolution of Hexamethylene diamine (HMDA, 0.35 g, 3.01 mmol) in water wasadded dropwise using a syringe and under stirring. The whole was left toreact at 50° C. for 1 hour and at 80° C. for 23 hours. FIG. 13 shows aphotograph of these microcapsules.

Example 12 Preparation of Thermochromic Microcapsules Based onPOSS@octa(acrylate) Monomer with Meta-Xylylenediamine

(i) Emulsion preparation

10.0 g of thermochromic, and polyoctahedral silsesquioxanes borne byeight acrylate functions (POSS@octa(acrylate), CAS No. 1620202-27-8,purchased from Hydridplastics, 1.50 g, 1.12 mmol) and ButylatedHydroxyToluene (BHT, 5.0 mg) thermal inhibitor, were placed in a beaker.The mixture was solubilized hot under magnetic stirring. Stirring wasmaintained until the solution became homogeneous. Thethermochromic/POSS@octa(acrylate) assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturraxm IKA T10 to form anemulsion.

(ii) Microencapsulation

In a reactor, the previously prepared emulsion was introduced. Thesolution of meta-xylylenediamine (CAS No. 1477-55-0, 0.60 g, 3.01 mmol)in 3 mL of water was added dropwise using a syringe and under stirring.The whole was left to react at 65° C. for 1 hour and at 80° C. for 17hours.

Example 13 Preparation of Thermochromic Microcapsules Based onPOSS@octa(acrylate) Monomer with POSS@Octammonium and HexamethyleneDiamine (HDMA)

(i) Emulsion Preparation

10.0 g of thermochromic, and polyoctahedral silsesquioxanes borne byeight acrylate functions (POSS@octa(acrylate), CAS No. 1620202-27-8,purchased from Hydridplastics, 1.40 g, 1.06 mmol) and ButylatedHydroxyToluene (BHT, 5.0 mg) thermal inhibitor, were placed in a beaker.The mixture was solubilized hot under magnetic stirring. Stirring wasmaintained until the solution became homogeneous. Thethermochromic/POSS@octa(acrylate) assembly was added gradually to thepreviously prepared aqueous surfactant solution (40 g, PVA 2 wt. %); themixture was homogenized using an Ultraturraxl™ IKA T10 to form anemulsion.

(ii) Microencapsulation

In a reactor, the previously prepared emulsion was introduced.Afterward, the solution of Hexamethylene diamine (HMDA, 0.70 g, 6.02mmol), POSS@(octa)ammonium (CAS No. 150380-11-3, purchased fromHydridplastics, 0.30 g, 0.26 mmol), and potassium carbonate (0.16 g,1.16 mmol) in water was added dropwise using a syringe, under stirring.The whole was left to react at 65° C. for 1 hour and at 80° C. for 17hours.

FIG. 14 shows a photograph of these microcapsules.

Example 14 Biodegradation Test

A batch of microcapsules prepared according to example 8 was provided.The dry microcapsules but containing essential oil (Eucalyptus) weresubjected to the biodegradability test described in the document OECD301 (“OECD Guidelines for Testing of Chemicals: Ready Biodegradability”)using method 301 F (Manometric respirometry test). After an incubationtime of nineteen days, the biodegradation percentage was 83%.

FIG. 15 shows the progression of the biodegradation percentage as afunction of time, over a 19-day duration. Curve (b) corresponds to themicrocapsule, while curve (a) corresponds to a reference product (sodiumacetate) processed separately under the same biodegradation conditions.

Example 15 Biodegradation Test

A batch of microcapsules prepared according to example 8 was provided.The microcapsules were opened, emptied and washed. Then they weresubjected to the biodegradability test described in the document OECD301 (“OECD Guidelines for Testing of Chemicals: Ready Biodegradability”)using method 301 F (Manometric respirometry test). After an incubationtime of twenty-eight days, the biodegradation percentage was 93%.

FIG. 16 shows the progression of the biodegradation percentage as afunction of time.

Example 16 Preparation of Fragranced Microcapsules Based on a Multiamine(Pentaethylenehexamine)

(i) Emulsion Preparation

19.7 g of essential oil (Eucalyptus) was placed in a beaker, and themulti-acrylate monomer (Dipentaerythritol penta-/hexa-acrylate mixture)(1.2 g, 2.29 mmol) was dispersed in the essential oil under magneticstirring (350 rpm) at 50° C. Stirring was maintained until the solutionbecame homogeneous. The essential oil/organic monomer assembly was addedgradually to the prepared aqueous surfactant solution (31.7 g, PVA 2 wt.%) previously heated to 50° C.; the mixture was homogenized using anUltraturrax™ IKA T10 at 11,500 rpm for 3 min at 50° C. to form anemulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, preheated to 50° C., the previously prepared emulsion wasintroduced and stirred at a speed of 250 rpm. The solution of multiamine(Pentaethylenehexamine) (1.9 g, 8.00 mmol) in 5.5 g of PVA 2 wt %solution was added dropwise using a syringe and under stirring (250rpm). The reaction mixture was kept under stirring for 2 hours at 50° C.then 5 hours at 60° C.

The total quantity of monomers used was 3.1 g. The amine was used inexcess with respect to the acrylate monomer so as to obtain anAmine/acrylate molar ratio=3.5. The essential oil/water mass ratio isequal to 0.53.

Example 17 Preparation of Fragranced Microcapsules Based on an AromaticDiamine (m-xylylene diamine)

(i) Emulsion preparation

22.0 g of fragrance was placed in a beaker, and the multi-acrylatemonomer (Dipentaerythritol penta-/hexa-acrylate mixture) (1.52 g, 2.90mmol) was dispersed in the fragrance under magnetic stirring (350 rpm)at 50° C. Stirring was maintained until the solution became homogeneous.The fragrance/organic monomer assembly was added gradually to thepreviously prepared aqueous surfactant solution (35.0 g, PVA 2 wt. %);the mixture was homogenized using an Ultraturrax™ IKA T10 at 11,500 rpmfor 3 min at 50° C. to form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, preheated to 65° C., the previously prepared emulsion wasintroduced and stirred at a speed of 250 rpm. When the emulsion hasreached 65° C., the solution of m-xylylenediamine (0.80 g, 5.88 mmol) in5.0 g of PVA 2 wt % solution was added dropwise using a syringe andunder stirring (248 rpm). The reaction mixture is kept under stirringfor 5 hours at 65° C. and 1 hour at 80° C.

The total quantity of monomers used was 2.3 g. The amine was used inexcess with respect to the acrylate monomer so as to obtain a—NH/acrylate function ratio=1.6. The fragrance/water mass ratio is equalto 0.55.

FIG. 17 shows a photograph of these microcapsules.

Example 18 Preparation of Fragranced Microcapsules with a CelluloseFiber Coating

(i) Emulsion Preparation

22.0 g of fragrance was placed in a beaker, and the multi-acrylatemonomer (Dipentaerythritol penta-/hexa-acrylate mixture) (1.52 g, 2.90mmol) was dispersed in the fragrance under magnetic stirring (350 rpm)at 50° C. Stirring was maintained until the solution became homogeneous.The fragrance/organic monomer assembly was added gradually to thepreviously prepared aqueous surfactant solution (40.0 g, PVA 2 wt. %);the mixture was homogenized using an Ultraturrax™ IKA T10 at 11,500 rpmfor 3 min at 50° C. to form an emulsion.

(ii) Microencapsulation

In a double-wall reactor, equipped with an IKA blade mechanical stirringsystem, preheated to 65° C., the previously prepared emulsion wasintroduced and stirred at a speed of 250 rpm. When the emulsion reached65° C., the solution of m-xylylenediamine (0.80 g, 5.88 mmol) in 5.0 gof PVA 2 wt % solution was added dropwise using a syringe and understirring (250 rpm). The reaction mixture is kept under stirring for 5hours at 65° C. and 1 hour at 80° C.

The total quantity of monomers used was 2.3 g. The amine was used inexcess with respect to the acrylate monomer so as to obtain a—NH/acrylate function ratio=1.6. The essential oil/water mass ratio isequal to 0.5.

(iii) Cellulose Coating

4 wt. % of cellulose microfiber (Exilva F 01-L) was preheated to atemperature between 65° C. and 70° C. then introduced into the hotslurry under stirring. The mixture is homogenized hot under stirring for30 min and for 2 hours at ambient temperature.

A cotton fiber bonding test was performed: a cotton fiber was previouslywetted and then steeped in the slurry. After washing vigorously andthoroughly in water to simulate rinsing, the fiber was dried at ambienttemperature.

FIG. 18 shows a photograph (image (b)) of a cotton fiber after steepingin a slurry solution then drying for microcapsules in which the surfacehas been modified. The coating enhances the bonding of the microcapsuleson the cotton fiber, compared to uncoated microcapsules (image (a)).

1. A method for manufacturing microcapsules containing a so-calledactive substance, in which method: an aqueous solution of a surfactant,an oily phase comprising said active substance and at least a firstmonomer X, and a polar phase comprising at least a second monomer Y areprovided; an O/W type emulsion is prepared by adding said oily phase tosaid aqueous solution of the surfactant; said polar phase is added tosaid O/W emulsion, in order to obtain a polymer by polymerizing saidmonomers X and Y; from this reaction mixture, said microcapsulesincluding a wall formed by said polymer and containing said activesubstance are isolated; said method being characterized in that saidpolymer is a poly(beta-amino ester).
 2. The method according to claim 1,characterized in that said first monomer X is selected from(multi)acrylates, and preferably (multi)acrylates of formulaX′—(—O(C═O)—CH═CH₂)_(n) where n≥4 and where X′ is a molecule whereon nacrylate structural units are grafted.
 3. The method according to claim2, characterized in that the first monomer X is selected from the groupformed by: diacrylates; triacrylates, particularly trimethylolpropanetriacrylate, tetraacrylates, pentaacrylates, hexaacrylates, mixtures ofthese different acrylates of type O[CH₂C(CH₂OR)₃]₂ where R is H orCOCH═CH₂; polymers carrying pendant acrylate functions; functionaloligo-PBAEs, prepared for example by reacting diacrylate compounds witha functional primary amine and/or a functional secondary diamine; themixture of different compounds described above.
 4. The method accordingto claim 1, characterized in that said second monomer Y is selected fromamines.
 5. The method according to claim 4, characterized in that thesecond monomer Y is selected from the group formed by: primary aminesR—NH₂; primary diamines of type NH₂(CH₂)_(n)NH₂ where n is an integerwhich can typically be between 1 and 20, and which is preferably 2 or 6;primary diamines having an aromatic core, and preferably meta-xylylenediamine; primary (multi)amines, and preferably tris(2-aminoethyl) amine;(multi)amines containing primary and secondary amine functions, andpreferably tetraethylene pentamine; secondary diamines and preferablypiperazine; polymers containing primary and secondary amine functions,and preferably polyethylene imine.
 6. The method according to claim 1,characterized in that said polymerization of said monomers is performedunder stirring at a temperature between 20° C. and 100° C., andpreferably between 30° C. and 90° C.
 7. The method according to claim 1,characterized in that said surfactant is selected from the group formedby macromolecular surfactants, preferably in that said surfactant isselected from the group formed by polyacrylates, methylcelluloses,carboxymethylcelluloses, polyvinyl alcohol optionally partiallyesterified or etherified, polyacrylamide, synthetic polymers havinganhydride or carboxylic acid functions, ethylene/maleic anhydridecopolymers, and in that said surfactant is even more preferablypolyvinyl alcohol.
 8. The method according to claim 1, characterized inthat said active substance is selected from the group formed by:essential oils, fragrances, inks, paints, thermochromic and/orphotochromic substances, dyes, adhesives, products with biocidal effect,products with fungicidal effect, products with antiviral effect,products with phytosanitary effect, products with cosmetic effect,pharmaceutical active ingredients, natural and edible oils, plant andedible oils, liquid alkanes, esters and fatty acids.
 9. The methodaccording to claim 1, characterized in that the wall of themicrocapsules is modified either by a layer of polymer deposited on thesurface of the microcapsule, or by adding a radical initiator in theaqueous phase and/or oily phase, or by adding in the aqueous phase awater-soluble acrylate capable of modifying the surface condition of themicrocapsules.
 10. A microcapsules prepared according to the method ofclaim
 1. 11. The microcapsule according to claim 10, containing aso-called active substance, characterized in that the wall thereofconsists of poly(beta-amino ester).
 12. The microcapsule according toclaim 10, characterized in that it has a mean diameter between 100 nmand 100 μm, preferably between 1 μm and 50 μm, and even more preferablybetween 10 μm and 40 μm.
 13. The microcapsule according to claim 10,characterized in that said microcapsule and/or the wall thereof shows abiodegradation of at least 80%, preferably at least 83%, and even morepreferably at least 85%, measured with a manometric respirometry testaccording to method 301 F of the “OECD Guidelines for Testing ofChemicals: Ready Biodegradability” after ten days of incubation.
 14. Themicrocapsule according to claim 10, characterized in that saidmicrocapsule and/or the wall thereof shows a biodegradation of at least90%, preferably at least 95%, and even more preferably at least 98%,measured with a manometric respirometry test according to method 301 Fof the “OECD Guidelines for Testing of Chemicals: ReadyBiodegradability” after 28 days of incubation.
 15. The microcapsuleaccording to claim 10, characterized in that the wall thereof has beenmodified either by a polymer layer deposited on the surface of themicrocapsule, or by adding a radical initiator in the aqueous phaseand/or the oily phase, or by adding in the aqueous phase a water-solubleacrylate capable of modifying the surface condition of themicrocapsules.